A seat belt system for restraining an occupant of a vehicle ordinarily includes seat belt webbing, a seat belt buckle, and a seat belt retractor. A tongue on the webbing is releasably lockable in the buckle when the webbing is extended around the vehicle occupant. The retractor includes a spool upon which the webbing is wound. The spool rotates in an unwinding direction when the vehicle occupant extracts the webbing from the retractor and moves the webbing toward the extended position in which the tongue is locked in the buckle. When the tongue is subsequently unlocked and released from the buckle, a rewind spring in the retractor rotates the spool in a winding direction to retract the webbing into the retractor.
The occupant may move forcefully against the webbing when the vehicle experiences a crash. The force that the occupant applies to the webbing urges the webbing to move outward from the retractor. Therefore, a seat belt retractor typically includes an emergency locking mechanism which is actuated in response to a vehicle crash condition. The emergency locking mechanism then blocks unwinding rotation of the spool to prevent the webbing from moving outward from the retractor.
An emergency locking mechanism may include an inertia weight. The inertia weight is movable under the influence of sudden vehicle deceleration that is caused by a crash. Such an emergency locking mechanism is actuated when the inertia weight moves from an unactuated position to an actuated position. Accordingly, the retractor is mounted in the vehicle in an orientation in which the inertia weight normally rests in the unactuated position.